Trimmer condenser



May 29, 1956 H. M. WADSWORTH 2,

TRIMMER CONDENSER Filed Nov. 25, 1953 2 Sheets-Sheet 1 WWW ' INVENTOR.

f/oward il/Zasworik WITNESS I Km. ZUK

A TORNEY y 1956 H. M. WADSWORTH 2,748,327

TRIMMER CONDENSER Filed Nov. 23, 1953 2 Sheets-Sheet 2 I V NTOR.

AT NEY TRIMMER CONDENSER Howard M. Wadsworth, Liverpool, N. Y.

Application November 23, 1953, Serial No. 393,605

6 Claims. (Cl. 317-249) The present invention relates to a trimmercondenser for high frequency oscillating circuits and more particularlyto an adjustable tubular type of miniature condenser.

It is an object of the present invention to provide a novel condenser ofthis type which is efiicient in operation, economical in construction,and of small dimensions in relation to its electrical capacity.

It is another object to provide such a device which is so constructed asto lend itself to a simple and rapid method of construction andassembly.

It is another object to provide a novel and effective method ofconstructing and assembling the trimmer condenser.

It is another object to provide a gang-tuned multiple unit of the abovetype.

It is another object to provide such a multiple unit in which one of theunits is readily adjustable to independently vary its capacity.

Further objects and advantages will be apparent from the followingdescription taken in connection with the accompanying drawing, in which:

Fig. 1 is a side elevation, partly broken away and in section, of apreferred embodiment of the invention;

Fig. 2 is a section taken substantially on the line 22 of Fig. 1;

Fig. 3 is a detail in perspective of the inner electrode of thecondenser as partially assembled;

Fig. 4 is a detail similar to Fig. 3 showing the inner electrode in itscompleted form;

Fig. 5 is a view similar to Fig. 1 showing a twin, gang-tuned trimmerconstructed in accordance with the present invention;

Fig. 6 is a detail in perspective of the inner metallic band formingpart of the outer electrode of the inde pendently adjustable condenser;

Fig. 7 is a similar view of the outer metal sleeve of the same;

Fig. 8 is a section on the line 88 of Fig. 5; and

Figs. 9, 10 and 11 are semi-diagrammatic developments of the parts ofthe independently adjustable outer electrode showing steps in theprogressive reduction in the effective area of the electrode.

In Fig. 1 of the drawing there is illustrated a tube 1 of suitabledielectric material having a cylindrical metallic band 2 fixedly mountedthereon to constitute the outer electrode of the condenser. Bushings 3and 4 are rigidly mounted in the ends of the tube 1 in any suitablemanner and serve to rotatably support at its ends a screw shaft 5 incoaxial relation with the tube 1. The bushing 3 is adapted to be mountedin a panel 6 to which it is aflixed by a clamp nut 7 or other suitablemeans.

As best shown in Fig. 4 the inner electrode comprises a slotted hollowcylinder 8 of elastically deformable material such as rubber, aroundwhich a band 9 of sheet metal is wrapped, with its ends traversing theslot 11 of the rubber tube and conformed to the interior of the tube.

- nited States Patent 6 Applicants novel method of constructing thisinner electrode comprises the steps of inserting one end of a suitablyproportioned metallic sheet or heavy foil through the slot 11 until itbottoms on the interior of the cylinder 8, then pressing through theslot 11 a cylindrical mandrel 12 having a diameter approximately thesame as the interior diameter of the cylinder 8 and having a slot 13which is arranged to register with the slot 11 in the rubber tube. Whenthe mandrel is so inserted, the rubber tube 3 is forced opensufliciently to receive the mandrel, and as the tube springs back to itsoriginal shape the inserted end of the metallic sheet 9 is caused toconform itself to the interior of the cylinder 8 as shown at 14 in Fig.3.

The said metallic sheet 9 is then wrapped around the cylinder 8 and itsother end inserted through the slot 11 of the cylinder into theregistering slot 13 of the mandrel 12 as shown at 15 in Fig. 3. Themandrel is then rotated in a clockwise direction whereby the sheet istightly contracted around the cylinder 8 and then the end 15 of thesheet is rolled into contact with the interior of the cylinder as shownin Fig. 4-.

The inner electrode so formed is mounted on the screw shaft 5 byintroducing the screw shaft endwise while rotating the screw shaft andsimultaneously withdrawing the mandrel as the screw shaft advances. Thethreads of the screw shaft thus form corresponding threads in the endportions 14 and 15 of the sheet 9 within the cylinder 8. If the sheet 9is of metal which is sufficiently softer then that of the screw shaft,the threads are scored in the portions 14 and 15, but if a harder metalis used such as a thin sheet of stainless steel, the material conformselastically to the threads of the screw shaft as permitted by theresiliency of the rubber tube, so that a threaded relationship of theinner electrode on the screw shaft is established.

The screw shaft with the inner electrode threaded thereon is theninserted in the dielectric tube 1, the dimensions of the parts being soproportioned that a suitable degree of compression is required to insertthe elec trode, whereby the threaded connection of the electrode on thescrew shaft is firmly maintained, and the metal lic sleeve 9 iselastically pressed against the interior of the tube 1. The assembly ofthe unit is completed by permanently attaching the bushings 3 and i tothe tube 1.

The screw shaft 5 is preferably provided with such as a screw driverslot 16 at both ends to facilitate adjustment at either end. It will beunderstood that rotation of the inner electrode will be prevented by itsfrictional engagement with the interior of the tube 1 since the radiusof its engaging surface is much larger than the radius of the screwshaft whereby rotation of the screw shaft will cause traversal of theinner electrode to bring it more or less into registry with the outerelectrode and consequently vary the capacity of the condenser.

In Fig. 5 of the drawing there is illustrated an adaptation ofapplicants invention to produce a gang type trimmer condenser; that is,a unit comprising a plurality of condensers which are capable of beingtuned simultaneously in step. As there illustrated two such units areprovided, one of the units which is indicated generally by numeral 20being of the same construction as the embodiment of the invention abovedescribed, the parts being similarly numbered.

The inner electrode of the second unit 21 is constructed in the samemanner as previously described, and in fact may, as illustrated, beformed as a unit with the inner electrode of the unit 20, both beingmounted on the same hollow rubber cylinder 8. The outer electrode of thesecond unit, which is indicated generally by the numeral 22, is soconstructed as to be adjustable independently of the first unit in orderto secure the proper relationship between the circuits to besimultaneously tuned. For this purpose, the outer electrode comprises astationary metallic band 23 (Fig. 6) which is provided with a series ofopenings 24, 25 and 26, and a metallic sleeve 2'7 (Fig. 7) also having aseries of openings 28, 29 and 31' therein is rot-stably mounted on theband 23 being kept from longitudinal movement by spinning over the endsof the sleeve 27 as indicated at 31 and 32.

The openings in the band 23 and sleeve 1.7 are arranged to be broughtprogressively into registry by rotary adjustment of the sleeve on theband, thereby varying the effective area of these members functioningtogether as the outer electrode of the unit 21. One suitable arrangementfor securing a progressive variation in the effective area of the outerelectrode 23, 27 is shown in section in Fig. 8, and three progressivesteps in such adjustment are illustrated in Figs. 9, l and 11. In Fig. 8the three openings 24, 25 and 26 in the band 23 are shown as occupyingan arc of 30, separated by arcs of 90. The openings in the outer sleeveare of graduated width and spacing, the opening occupying an arc of 30and being separated from the opening 29 by an arc of 90. The opening 29has a width of 60 and is separated from the opening 30 by an arc of 60.The opening 30 has a width of 90 and is separated from the opening 28 byan arc of 30. it will thus be seen by examination of Figs. 9, 10 and 11that rotation of the outer sleeve from the position shown in Fig. 8wherein all the openings in the band 23 are covered will progressivelyuncover openings 2d, 25 and 215, thus correspondingly reducing theeffective area of the electrode to a minimum as shown in Fig. 11.

In some cases, it may be found desirable to insulate the innerelectrodes of one or both of the units 20, 21 from the screw shaft andprovide individual flexible electrical connections to each electrode.This is conveniently acco :plished by introducing a flexible splitsleeve of suitable dielectric material such as nylon as indicated at 33in Figs. and 8. In such case, the nylon sleeve may perform tie functionof the slotted mandrel 12 of Fig. 3 in the assembly of the electrode,the nylon being of course left in place and the screw shaft threadedtherein prior to assembly in the dielectric tube. If found desirable,the nylon sleeve may be formed with terminal flanges 3d and 25, and oneor more longitudinal ribs 36 in order to positively prevent relativemovement between the sleeve and rubber cylinder.

While certain structure has been shown and described in detail it willbe understood that other embodiments are possible and that changes maybe made in the design and arrangement of the parts without departingfrom the spirit of the invention.

I claim:

1. In a tubular trimmer condenser a dielectric tube having an outermetal envelop constituting one electrode, a screw shaft rotatablymounted coaxially in said tube, and an inner electrode mounted on thescrew shaft comprising a slotted hollow cylinder of elasticallydeformable rubher-like material and a sheet of electrically conductivematerial wrapped around said cylinder and pressed into full surfacecontact with the interior of the dielectric tube by the expansion of theelastically deformable material, and with its end portions entering thecylinder through the slot and embracing the screw shaft, said endportions being expanded into conformity with the interior surface of theelastic cylinder to serve as anchorages maintaining said conductivesheet under tension around the exterior of said cylinder.

2. A trimmer condenser as set forth in claim 1 in which the innerelectrode is compressed within the dielectric tube sufficiently to causethe threads of the screw shaft to form corresponding threads in theembracing ends of the conductive material.

3. A trimmer condenser as set forth in claim 1 including further a splitsleeve of dielectric material interposed between the electricallyconductive material and the screw shaft to insulate the inner electrodefrom the shaft while serving to impart longitudinal movement to theinner electrode responsive to rotation of the screw shaft.

4. A trimmer condenser as set forth in claim 3 in which the sleeve ofdielectric material is provided with means for positively impartinglongitudinal movement to the inner electrode and preventing relativerotary movement.

5. In a method of constructing and assembling a tubular trimmercondenser, the steps of forming an inner electrode by inserting one endof a thin sheet of metal into a hollow slotted cylinder of rubber or thelike, forcing a slotted mandrel into the cylinder to press said end intoconformity with the interior of the cylinder, wrapping the metallicsheet around the rubber cylinder, inserting the other end of said sheetthrough the slot of the cylinder and into the registering slot of themandrel, and then rotating the mandrel in the cylinder to draw the sheettightly around the cylinder and cause said other end of the sheet toalso conform to the interior of the cylinder.

6. In the method set forth in claim 5 the additional steps of formingand assembling the inner electrode including withdrawing the mandrelendwise from the cylinder While threading a screw shaft after it, andthen inserting this sub-assembly in a dielectric tube which carries theouter electrode of the condenser.

References Cited in the file of this patent UNITED STATES PATENTS2,541,897 Wadsworth Feb. 13, 1951 2,544,550 Bird Mar. 6, 1951 2,589,092Kihn Mar. 11, 1952 FOREIGN PATENTS 458,710 Great Britain Dec. 24, 1936541,712 Great Britain Dec. 8, 1941 608,084 Germany Jan. 15, 1935 628,499Germany Apr. 6, 1936

